1. Untagged template literals don't call @@toPrimitive correctly
   • See Template Literals Incorrect babel/babel#1065 (which is still has parts incorrect)
   • See Spec compatibility for template literals. babel/babel#5791 (which fixes symbols via concat grouping)
2. Tagged template literals need to have the entire TemplateStringsArray frozen
   • The cooked is currently still mutable
3. The TemplateStringsArray must be cached per call site
   • See Babel REPL

As a bonus, there's a small size win that you can get if the cooked and raw are the same (there are no \ escape sequences), see babel/babel#7352.